1. Field of the Invention
The present invention relates to a process for forming a pattern of a semiconductor device used in a liquid crystal display apparatus and a method for producing a liquid crystal display apparatus using the process for forming a pattern, and in particular, to a process for forming a complex pattern, such as wirings, in a simplified manner and a method for producing a liquid crystal display apparatus using the process for forming a pattern.
2. Description of the Prior Art
A process for producing a liquid crystal display apparatus uses a photolithography technique and a dry etching technique that are used for producing an integrated circuit. Therefore, as is seen in activities to reduce process steps for producing the integrated circuit, in the process for producing a liquid crystal display apparatus, efforts in reducing the number of the total process steps for forming patterns, such as wirings, are exercised as well to reduce the production cost thereof.
A method for reducing the process steps for forming patterns employed for forming wirings in the conventional technique will be described.
In the conventional process for forming wirings, as shown in FIG. 1A, a gate electrode 802 is formed on a glass substrate 801 by the known photolithography technique and the known etching technique. Then, a gate insulating film 803, an amorphous silicon film 804, an n+ type amorphous silicon film 805 and a metal film 806 are successively deposited to form a laminated structure.
As shown in FIG. 1B, mask patterns 821 and 851 made of a photoresist are formed on the metal film 806 by the known photolithography technique, and the metal film 806 and the n+ type amorphous silicon film 805 are sequentially subjected to dry etching by using the mask patterns 821 and 851 as a mask. As a result, ohmic contact layers 805 and 835, a source electrode 806 and a drain electrode 836 are formed on the amorphous silicon film 804 as shown in FIG. 1C.
Thereafter, the mask patterns 821 and 851 are removed as shown in FIG. 1D, and then a mask pattern 822 is formed to cover the ohmic contact layer 805, the source electrode 806, the ohmic contact layer 835, the drain electrode 836 and a part of the surface of the film 804 as shown in FIG. 2A.
As shown in FIG. 2B, by using the mask pattern 822 as a mask, the underlying amorphous silicon film 804 is selectively removed by etching to form a semiconductor island 834, in which a channel is to be formed later on.
Thereafter, the mask pattern 822 is removed as shown in FIG. 2C, whereby such a state is obtained that an inversely staggered TFT is formed on the glass substrate 801. A pixel electrode and a passivation insulating film, for example, are then formed, so as to constitute an active matrix TFT substrate of a liquid crystal display apparatus.
However, in the conventional method for producing an active matrix TFT described above, the semiconductor layer, in which a channel is to be formed, needs to be formed in the form of an island on an insulating substrate made of a glass or the like to forma TFT. Therefore, it is concluded that the conventional method for producing an active matrix TFT needs an additional photolithography step in comparison to the production process of a general MOSFET, thereby increasing the production cost thereof.